trillion

Trillion is a large number whose exact value depends on the numbering system in use. In the short scale, which is standard in the United States and in most modern English-language contexts, a trillion equals 1,000,000,000,000 (10^12). In the long scale, historically used in parts of Europe, a trillion equals 1,000,000,000,000,000,000 (10^18).

These different scales create ambiguity in cross-cultural usage. In the long scale, a billion is 10^12 and a trillion is 10^18; in the short scale, a billion is 10^9 and a trillion is 10^12. Over the past century many countries have shifted toward the short scale for common usage, but the long scale remains in use in some contexts or languages, and older texts may reflect the long-scale definitions.

Etymology traces trillions and related terms to the word trillion from French, ultimately from Italian trilione, built from tri- meaning three and -illion, a form associated with million. The naming reflects historical conventions rather than a universal literal meaning, contributing to ongoing confusion without explicit clarification of which scale is intended.

In scientific and technical writing, precision is preferred over traditional names. The decimal prefixes of the International System of Units (SI) are unambiguous: 10^12 corresponds to tera-, and 10^18 corresponds to exa-. Thus 1 × 10^12 is a trillion in the short scale, whereas 1 × 10^18 aligns with the long-scale sense of trillion.